Hindawi Publishing Corporation Journal of Osteoporosis Volume 2013, Article ID 679025, 6 pages http://dx.doi.org/10.1155/2013/679025

Review Article Nanohydroxyapatite Application to Osteoporosis Management

Zairin Noor

Department of Orthopaedics and Traumatology, Ulin General Hospital, Faculty of Medicine, University of Lambung Mangkurat, 70232 Banjarmasin, South Kalimantan, Indonesia

Correspondence should be addressed to Zairin Noor; [email protected]

Received 22 July 2013; Accepted 8 September 2013

Academic Editor: S. Minisola

Copyright © 2013 Zairin Noor. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Hydroxyapatite is chemically related to the inorganic component of matrix as a complex structure with the formula of Ca10(OH)2(PO4)6. Previous studies have reported the application of microsized hydroxyapatite to bone regeneration, but the result is not satisfied. The limitation comes from the size of hydroxyapatite. In addition, the duration of treatment is very long. The advantages of hydroxyapatite nanocrystal are the osteoconduction, bioresorption, and contact in close distance. Crystal in osteoporotic bone is calcium phosphate hydroxide with the chemical formula of Ca10(OH)2(PO4)6. Crystal of normal bone is sodium calcium hydrogen carbonate phosphate hydrate with the chemical formula of Ca8H2(PO4)6⋅H2O–NaHCO3–H2O. The recent development is applying nanobiology approach to hydroxyapatite. This is based on the concept that the mineral atoms arranged in a crystal structure of hydroxyapatite can be substituted or incorporated by the other mineral atoms. In conclusion, the basic elements of hydroxyapatite crystals, composed of atomic minerals in a certain geometric pattern, and their relationship to the bone cell biological activity have opened opportunities for hydroxyapatite crystals supplement application on osteoporosis. Understanding of the characteristics of bone hydroxyapatite crystals as well as the behavior of mineral atom in the substitution will have a better impact on the management of osteoporosis.

1. Background of an immune response and disease transmission (HIV and hepatitis B) to the recipient. Bone substitute graft attracts Bone is an organic-inorganic ceramic composite containing attention among experts due to the advantages that go beyond well-structured fibrils, nanocrystalline, and rod- autograft and allograft. Biomineral morphogenesis is aspe- like inorganic material with length of 25–50 nm. Sequence cific strategy in the development of architectural construction of bone structure is formed from seven levels of hierarchy of chemical compounds in microsize and nanocrystal [2]. and reflects the material and mechanical properties of each Clinically, osteoporosis is identified through nontrau- component. Hydroxyapatite is chemically related to inor- matic/minimal fracture in the vertebra, hip, proximal hu- ganic component of bone matrix as a complex structure with merus, and femur fracture. Osteoporosis is a disorder specif- formula Ca10(OH)2(PO4)6.Similarityofchemicalcompound ically found in elderly men and women [3–6]. Increased of the hydroxyapatite to the bone has triggered intensive economy and aging population will increase the frequency of researches on the use of synthetic hydroxyapatite as bone osteoporosis so that it becomes an essential health issue [5, 7]. substitution and/or bone repositioning for biomedical appli- This paper will discuss the development of a synthetic cations [1]. materialasabonesubstitutegraftandthepotentialsof Intrabone defect is a challenge for clinicians. This defect hydroxyapatite microcrystals and nanocrystals, as well as only requires flap surgery or is associated with other tech- hydroxyapatite nanocrystal applications as a method of filling niques. Bone substitution is necessary to repair segmental bone defect in osteoporosis. defects caused by the removal of infected tissues or bone tumor. Bone substitution mostly required in the particular 2. Synthetic Materials case is autologous bone. However, autograft is not always available and may cause morbidity in donor site. Allograft Thereareavarietyofsyntheticmaterialsusedinbone may be an alternative in some cases, but there is the possibility substitute graft, including metal, tantalum, titanium, iron, 2 Journal of Osteoporosis magnesium; polymers such as polylactide, polyglycolide, microcrystals can accelerate fracture healing and repair and polyurethane, or polycaprolactone; and ceramics such as even prevent osteoporosis [9]. silica-based glass, calcium sulfate hemihydrate (CSH or plaster of Paris) and dihydrate (CSD or gypsum), and calcium 6. Hydroxyapatite Nanocrystal phosphate. Of these materials, calcium phosphate-based materials are very attractive. Based on its similarity to the Recent development in biomaterial research focuses on the composition of the bone structure (about 60% is calcium limitations of calcium phosphate ceramics and improved phosphate), the material was considered for the first time, bioreactivity through the use of nanotechnology. Bone graft since a century ago, and has been widely studied as a bone of synthetic hydroxyapatite nanocrystal has been introduced substitution for 40 years [8]. in bone defect repair procedure. The advantages of hydrox- yapatite nanocrystal are osteoconduction, bioresorption, and contact in close distance. Typical description of materials 3. Bone Grafts with nanostructures is a very high number of molecules on the surface of the material. When hydroxyapatite nanocrystal Most of the bone substitute grafts used are granules (diameter is used as a bone substitute graft, rapid healing of critical between 0.1 to 5 mm) or porous blocks (or sponges). Some size defect has been demonstrated in animal experiments and formulas may harden after implantation in situ or injection. applications in humans. Hydroxyapatite nanocrystals will Formulae with such properties, among others, are calcium be bound to the bone and stimulate bone healing through sulfate hemihydrate (plaster of Paris) and phosphate calcium the stimulation of osteoblast activity. Nonetheless, hydrox- cement. Reaction setting of this material was initiated by yapatite nanocrystal is difficult to form specific formula mixing the powder with the liquid solution. Chemically, needed for bone repair and implantation. This is due to hardening occurs due to the success of dissolution and theintrinsichardness,fragility,andlackoftheflexibility, precipitation reactions. Mechanically, hardening is caused by thereby restricting the use of a load-bearing implant material. entanglement and intergrowth of crystals [8]. Therefore, hydroxyapatite nanocrystal is often combined with Possible injection of bone substitute graft has extended various polymers to produce osteoconductive biocomposite its application, for example, the treatment of bone fractures material in the field of orthopedic surgery [1, 10]. in minimally invasive surgery. In addition to pasta, porous blocks, and pasta that can be hardened, bone substitute graft canalsoformapastethatcannotbehardened(=putty).This 7. Hydroxyapatite Crystals in Osteoporosis material is a combination of the granules and the “glue” as a highly viscous hydrogel [8]. Osteoporosis is a disorder that causes a decrease in bone mass that is normally mineralized due to an imbalance between osteoclast and osteoblast activities [3–5]. Osteoporosis is an 4. Hydroxyapatite Potentials amorphous process due to the irregular degenerative process, which is difficult to characterize, within a wide range of bone Nowadays, hydroxyapatite is widely used in biomedical mineralization. Change in bone mineralization is strongly applications, including matrices to control drug release and influenced by the nature of atoms capable of performing a material engineering of bone tissues. Based on the chemical substitution to form a composite as seen in Figure 1 [6, 7]. similarities between the hydroxyapatite and inorganic com- Solid material is described as amorphous and crystalline ponent of bone matrix, synthetic hydroxyapatite has a strong material. An amorphous material when its atoms are ran- affinity to host hard tissues. Chemical bond between the domly arranged will be similar to the iron atoms in the liquid. host and hydroxyapatite causes this material to become clin- Crystalline materials where the atoms are arranged in a regu- ically a beneficial application, which is better than allograft lar pattern with the smallest element in a three-dimensional or metal implants. The main advantages of hydroxyapatite replication will form crystals [11]. Bone crystals are extremely are biocompatibility, low in situ biodegradation, and good small,withameanlengthof50nm(withinrangeof20– osteoconduction. In addition, hydroxyapatite also has good 150 nm), an average width of 25 nm (in range of 10–80 nm), biocompatibility to the soft tissues, such as and muscles. and a thickness of only 2–5 nm. Apatite phase contains 4–8% Synthetic hydroxyapatite is currently widely used for hard carbonate by weight, referred to as dahlite. Mineral composi- tissue repair. Hydroxyapatite is commonly used in bone tion will vary with age and is always subject to calcium defi- repair as bone addition, coating implants and bone fillers1 [ ]. ciency where carbonate and phosphate ions are in the crys- tal lattice. Formula Ca8.3(PO4)4.3(CO)3𝑥(HPO4)𝑦(OH)0.3 5. Hydroxyapatite Microcrystals reflects the average composition of the bone, where y de- creases and x increases with age, whereas the addition x + Calcium hydroxyapatite microcrystal is a natural extract of y will be constant and equal to 1.7. Mineral crystal growth bone calcium. Calcium hydroxyapatite microcrystal contains occurs under specific orientation in which the c-axis of the anumberofmineralsinphysiologicalproportionsalong crystal is approximately parallel to the length axis of the col- with other bone organic minerals. Evidence suggesting that lagen fiber where the crystal deposition takes place. Electron calcium hydroxyapatite microcrystal is better absorbed than microscopic technique is used to obtain this information [12]. calcium supplements has triggered a variety of clinical XRD characterization results with the nanopowder pro- applications. Oral administration of calcium hydroxyapatite duction method using High Energy Milling then simulated Journal of Osteoporosis 3

Ca10(PO4)(OH)2 ??

Ca, Sr, Ba, Cd, Pb, Mg, Mn, Na, K, H, D,...... P, C O 3, V, As, S, Si, Ge, Cr, B,... Ag, Rb, La, Pd, Te, Yb, Re, Hf

OH, OD, CO3, O, BO2, F, Cl, Br,...

Figure 1: Some compositional possibilities can match the apatite structure. This is the phenomenon that provides a high compositional variation as a reference to the nonstoichiometric character. Besides, there are several atomic minerals which have unknown effect on hydroxyapatite crystals [12–15].

(a) (b) Figure 2: Crystal structure of normal bone (a) and osteoporotic bone (b). Normal crystal structure of the sodium calcium hydrogen carbonate phosphate hydrate with chemical formula Ca8H2(PO4)6⋅H2O–NaHCO3–H2O. Crystal structure of osteoporotic bone is the calcium phosphate hydroxide with chemical formula Ca10(OH)2(PO4)6⋅ The difference lies in the number of calcium atoms (local hypermineralization) and the presence of H2O–NaHCO3–H2O (substitution/incorporation) [14]. usingCrystalMakerSoftwareasshowninFigure2,shows bone. This indicates that the osteoporotic bone crystal has that the peak found is the peak of hydroxyapatite crystals, and irregular atomic arrangement or amorphous arrangement. no other crystalline phases were detected. Crystal in osteo- For normal bone, the arrangement of atoms in a hexagonal porotic bone is calcium phosphate hydroxide with chemi- structure has regularity. Besides the atom density of osteo- cal formula of Ca10(OH)2(PO4)6. Crystal of normal bone poroticbonecrystalsissmallerthanthatofnormalbone. is sodium calcium hydrogen carbonate phosphate hydrate Hexagonal crystal structure has a length or crystal lattice ∘ with chemical formula of Ca8H2(PO4)6⋅H2O–NaHCO3– parameter a = b ≠ c, while the angle 𝛼 = 𝛽 =90 and angle 𝛾 ∘ H2O[14]. The results of search and match test of both =120. This finding is consistent with a study by Sastry etal. normal bone and osteoporotic bone samples show crystalline [16], suggesting that the crystallinity of osteoporotic bone phase with hexagonal structure. Atom density in osteoporotic decreased. bone is lower (0.0841 atom/A)˚ compared with normal bone (0.0994 atom/A).˚ Osteoporotic bone crystal size is smaller than normal bone. Furthermore, crystallinity of osteoporotic 8. Potential of Hydroxyapatite in Osteoporosis bone is smaller than normal bone [14]. Crystal size in osteoporotic bone is smaller than that in Ossein microcrystalline hydroxyapatite is a combination of normal bone. This is presumably due to the irregular atomic organic and inorganic components. Inorganic components arrangement in the osteoporotic bone crystal in which crys- will provide calcium and phosphorus in the physiological tallographic parameters in osteoporotic bone are not known, ratio 2 : 1. The organic components include collagen and while in normal bone, crystallographic parameters are known noncollagen proteins with various growth factors and bone well in the form of hexagonal crystal system. Moreover, osteo- specific proteins, such as insulin-like growth factors I and porotic bone crystal showed a lower crystallinity than normal II, transforming growth factor (TGF-𝛽), and osteocalcin. As 4 Journal of Osteoporosis an alternative to calcium, ossein hydroxyapatite compound is not satisfied. The limitation comes from the size of hydroxya- a complex protein mineral that has higher osteogenic effect patite. In addition, the duration of treatment is very long. The when compared with mineral compounds or calcium sup- recent development is applying the nanobiology approach plement administered orally. Ossein hydroxyapatite provides to hydroxyapatite, although more studies are warranted benefits in the treatment and prevention of osteopenia and especially its affinity. Nanobiology approach comes from the osteoporosis in women, including primary and secondary concept that the mineral atoms arranged in a crystal struc- osteoporosis. Various studies suggest that ossein hydroxya- ture of hydroxyapatite can be substituted or incorporated patite is more effective than calcium carbonate in reducing by the other mineral atoms. A study by Noor et al. [13] bone loss in postmenopausal women and in preventing bone who performed mineral atomic substitution modeling in loss as well. bone hydroxyapatite crystals among Indonesian population showed changes in porosity and density of hydroxyapatite AstudybyCastelo-Brancoetal.[17]provedthatthe crystals in various mineral atomic substitutions. Some studies administration of ossein hydroxyapatite at a dose of 3.32 also applied substitution of magnesium [21], silicon [22], zinc gram/day compared to calcium carbonate at 2.5 mg/day for [23], iron [24], fluoride [25], chloride [26], carbonate [27], 12 and 24 concluded that no change in bone mass is found and strontium [28] in hydroxyapatite crystals. The results to be related to the baseline condition in the administration demonstrated changes in the physicochemical properties and of ossein hydroxyapatite, while the administration of calcium biological response of nanohydroxyapatite crystals. carbonatefoundasignificantdecreaseinbonemassinthe One benefit of nanocomposite is its ability to assemble second year. The study by Pelayo et al. [18]statedthatthe with other molecules. These properties will increase the combination of ossein hydroxyapatite and raloxifene was quality of osteoporosis management although need further more effective than a combination of ossein hydroxyapatite study. In the present work, the bone regeneration potential of and calcium carbonate in controlling bone loss among post- nanohydroxyapatite/chitosan composite scaffolds was com- menopausal women. A study by Albertazzi et al. [19]that paredwiththatofpurechitosanscaffoldswhenimplanted compared ossein hydroxyapatite with tricalcium phosphate into segmental bone defects in rabbits. Critical size bone at a dose of 500 mg/kg body weight in the prevention of bone defects (6 mm diameter, 10 mm length) were created in loss found that, in the third and sixth months, ossein hydrox- the left femoral condyles of 43 adult New Zealand white yapatite and tricalcium phosphate reduced bone formation rabbits. The femoral condyle bone defects were repaired by markers significantly compared with placebo. In the sixth nanohydroxyapatite/chitosan compositions, pure chitosan, month, tricalcium phosphate reduced osteocalcin by 9.9% or left empty separately. Defect-bridging was detected by and ossein hydroxyapatite by 12.3%. In addition, they found plain radiograph and quantitative computer tomography at a decrease in propeptide of type 1 procollagen (PINP) of 5.3% eightand12weeksaftersurgery.Tissuesampleswerecol- (tricalcium phosphate) and 6.3% (ossein hydroxyapatite). lected for gross view and histological examination to deter- Alkaline phosphatase also decreased by 4.3% (tricalcium mine the extent of new bone formation. Eight weeks after phosphate) and 6.7% (ossein hydroxyapatite). Effects on bone surgery, more irregular osteon formation was observed in the resorption markers and bone mineral density did not differ group treated with nanohydroxyapatite/chitosan composites 𝑃 > 0.05 significantly ( ). compared with those treated with pure chitosan. Twelve In randomized, open-label, parallel-group, controlled, weeks after surgery, complete healing of the segmental bone and prospective study, we compare the effects of OHC (treat- defect was observed in the nanohydroxyapatite/chitosan mentgroup)andcalciumcarbonate(controlgroup)onbone group, while the defect was still visible in the chitosan metabolism (followed up for a maximum of 3 years). Subjects group, although the depth of the defect had diminished. were women aged >65 years with densitometric osteoporosis These observations suggest that the injectable nanohydrox- of the lumbar spine or femoral neck. The treatment group yapatite/chitosan scaffolds are potential candidate materials received open-label OHC (osteoporosis) at a dose of two for regeneration of bone loss [29]. In addition, experiments 830 mg tablets every 12 hours (712 mg elemental calcium have shown that one of the mechanisms of the contact action per day). The control group received open-label calcium of nano-HAP on bacteria Staphylococcus aureus consists carbonate at a dose of 500 mg of elemental calcium every 12 in adhesion of nanocrystals on bacteria with subsequent hours (1000 mg elemental calcium per day). Both groups also formationofananostructureofparticlesofreactionproducts received a vitamin D supplement (calcifediol 266 𝜇g) at a dose hindering the enlargement and division of bacteria [30]. of one vial orally every 15 days. This study found that levels of serum osteocalcin increased to a greater extent in the OHC 9. Conclusion group compared with the calcium carbonate group. Changes over time in serum osteocalcin level were also statistically Thebasicelementsofhydroxyapatitecrystalscomposed significant𝑃 ( < 0.05) in the OHC group, but not in the of atomic minerals in certain geometric pattern and their calcium carbonate group. Besides, changes in mean BMD relationship to bone cell biological activity have opened at the lumbar spine and femoral neck between baseline and opportunities for hydroxyapatite crystals supplement appli- year 3 were −1.1% and 2.5% for OHC and −2.3% and 1.2% for cation to osteoporosis. Understanding of the characteristics calcium carbonate, respectively [20]. of bone hydroxyapatite crystals as well as the behavior of Previous studies have reported the application of micro- mineral atom in the substitution will have a better impact on sized hydroxyapatite to bone regeneration, but the result is the management of osteoporosis in the world. Journal of Osteoporosis 5

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